Well, new join module and still in English (or Polish).
Since you know that the join process in the first hazard to pass for newcomers, this is the very first part of Wikidot to be translated. Later, a well-built wikidot website can prevent displaying too much English, but not at this very first step.

It would be possible to get the language from the accessed page where the meta for language was set and then popup the join / sign in / create account in the appropriate language. (Do not do it with IP address ranges !).